I don't have a machine shop so no lathe. Can the AR bolt face be opened with an existing mill bit to fit the 7.62X25 Tok rim?

Yes.......I have opened a BUNCH......LOL....send it to me and I'll be happy to do it for you rudyk@maconarmory.com and 7.62 tok works great with the 5.56 extractor......
To do it sucessfully you need to set up in a 4 jaw on a lathe and indicate on the firing pin hole....then open up with a single point VERY RIGID CARBIDE stubby boring bar, because of the interrupted cut caused by the extractor slot.......and the extreme hardness of the bolt....it is real easy to get over size. It can be plunge cut on a mill but it requires a purpose ground mill (flat base non center cutting to do it right and if the ways are worn on your mill....it can turn into a mess real quick.